Bar compositions comprising soap, synthetic surfactant (e.g., acyl isethionate), free fatty acid and organic salts (e.g., sodium isethionate, sodium citrate) are known in the art.
U.S. Pat. No. 4,663,070 to Dobrovolny et al. and U.S. Pat. No 4,695,395 to Caswell et al. for example, teach such compositions comprising 30% to 70% by wt. neat soap, 5% to 45% acyl isethionate, free fatty acid and sodium isethionate. By contrast, however, the amount of synthetic surfactant used in the compositions of the subject invention is less than 5%, preferably less than 4%, more preferably less than 3%, more preferably less than 2%, most preferably less than 1% by wt. and may be absent altogether. The amount of synthetic used in Dobrovolny is much higher.
U.S. Pat. No. 5,030,376 to Lee et al. also claims cleaning compositions comprising 20 to 80% fatty acid soap (mixture of tallow and coconut), 10% to 60% by wt. C8 to C18 fatty acyl isethionate and 1% to 6% by wt. electrolyte (e.g., organic salt) which may be sodium isethionate. Also, 1 to 20% free fatty acid is in the composition. Again, the synthetic surfactant comprises at least 10% by wt. composition in contrast to the amount of synthetic in the compositions of the invention being under 5%.
GB Patent 2,317,396 (to Cussons Int.) teaches bars with 30 to 90% soap, 1% to 35% secondary surfactant and combination of at least two materials which may be fatty acids, fatty alcohol and hydrocarbons of melting point above 25.degree. C. (e.g., paraffin). There is no teaching or suggestion of adding the organic salts of the present invention in the GB patent.
In applicants copending application to Chambers et al., filed with British priority on Feb. 23, 1998, there is taught a specifically identified alkali metal soap; 3 to 35% fatty acid; 2 to 25% structurant; and water. There is no teaching of organic salts such as sodium isethionate or any teaching of the relationship between such salts and fatty acid in providing consumer benefits (as noted below).
Since synthetic surfactants (e.g., acyl isethionate, alkyl glycerol ether sulfate) are generally much milder than soap, one of the main reasons synthetic surfactant has been added to soap bars is to produce milder bars. The problem is that synthetic surfactants are also generally more expensive than soap.
One way of reducing the cost associated with synthetic surfactants is to replace some of the synthetic surfactant with free fatty acids. Such bars are known as superfatted bars. Unfortunately, substituting free fatty acid for synthetic surfactant, while this does possibly enhance mildness, may lead to the creation of bars with poorer user properties. Specifically, bars superfatted with long chain fatty acid, in the absence of the specific organic salts of the invention, tend to be tacky (e.g., extremely sticky, either to hands or equipment), to have noticeable discoloring and to have low lather.
In addition, a person of ordinary skill in the art would be disinclined to use any electrolyte (e.g., the specific organic salts of invention) in predominantly soap bar compositions because high (i.e., greater than 1%) levels of any electrolyte (e.g., organic or inorganic salts) have historically proven detrimental to the processability of these bars. Specifically, at high levels of, for example, sodium chloride, there is no cohesiveness between soap flakes formed when the flakes are extruded and the bars formed tend to become very brittle and "cracked" (see Comparative Examples 4 and 5).
In short, in the absence of the specific organic salts of the invention, there is no incentive to replace synthetic surfactant with free fatty acids because bars with little or no synthetic surfactant have poor user properties (especially in presence of a large amount of free fatty acid); yet there has been no incentive in the art thus far (in fact there has been teaching away) from using electrolyte of any kind (including organic salts) in such bars because high levels of electrolyte (e.g., inorganic alkali metal salts) are known to cause brittle bars which are difficult to process.